Laserless optical transceiver

ABSTRACT

An optical module includes an optical source, a first polarization splitter-rotator, a second polarization splitter-rotator, a first port, a second port, a third port, and a fourth port. The optical source produces an optical signal. The first polarization splitter-rotator generates a first source optical signal based at least in part on the optical signal. The second polarization splitter-rotator generates a second source optical signal based at least in part on the optical signal. The first port transmits, to a first device, the first source optical signal and receives, from the first device, a first modulated optical signal. The first polarization splitter-rotator produces a second modulated optical signal. The second port transmits, to a second device, the second source optical signal and receives, from the second device, a third modulated optical signal. The second polarization splitter-rotator produces a fourth modulated optical signal.

TECHNICAL FIELD

Embodiments presented in this disclosure generally relate to opticaldevices. More specifically, the embodiments relate to laserless opticaltransceivers.

BACKGROUND

Optical signals (e.g., lasers or lights) may be used to communicate dataor other information to optical devices. An optical source (e.g., alaser diode) may be used to source these optical signals. The opticalsources, however, also generate or may be sensitive to heat energy,which may be undesirable in certain circuits or designs.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate typicalembodiments and are therefore not to be considered limiting; otherequally effective embodiments are contemplated.

FIG. 1 an example optical system;

FIG. 2 illustrates example components of the optical system of FIG. 1 ;

FIG. 3 illustrates example components of the optical system of FIG. 1 ;

FIG. 4 illustrates an example optical system;

FIG. 5 is a flowchart of an example method performed in the opticalsystems of FIGS. 1 and 4 ;

FIG. 6 illustrates an example optical system;

FIG. 7 illustrates an example pluggable device in the optical system ofFIG. 6 ;

FIG. 8 illustrates example components of the optical system of FIG. 6 ;and

FIG. 9 is a flowchart of an example method performed in the opticalsystem of FIG. 6 .

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially used in other embodiments withoutspecific recitation.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

According to an embodiment, a system includes a first device and asecond device. The first device generates a source optical signal usinga first optical signal and a polarization splitter-rotator. The seconddevice modulates the source optical signal from the first device using afirst data signal to produce a first modulated optical signal. The firstmodulated optical signal has a polarization that is orthogonal to apolarization of the source optical signal. The first device recovers thefirst data signal from the first modulated optical signal using at leastthe polarization splitter-rotator.

According to another embodiment, a method includes generating, by afirst device, a source optical signal using a first optical signal and apolarization splitter-rotator and modulating, by a second device with anoptical connection to the first device, the source optical signal fromthe first device using a first data signal to produce a first modulatedoptical signal. The first modulated optical signal has a polarizationthat is orthogonal to a polarization of the source optical signal. Themethod also includes recovering, by the first device, the first datasignal from the first modulated optical signal using at least thepolarization splitter-rotator.

According to another embodiment, a system includes a first single modefiber, a first device, and a second device. The first device isconnected to the first single mode fiber. The first device generates asource optical signal using a first optical signal and a polarizationsplitter-rotator. The second device is connected to the first singlemode fiber. The second device modulates the source optical signalreceived from the first device over the first single mode fiber using afirst data signal to produce a first modulated optical signal. The firstmodulated optical signal has a polarization that is orthogonal to apolarization of the source optical signal. The first device receives thefirst modulated optical signal from the second device over the firstsingle mode fiber and recovers the first data signal from the firstmodulated optical signal using at least the polarizationsplitter-rotator.

According to an embodiment, an optical module includes an opticalsource, a first polarization splitter-rotator, a second polarizationsplitter-rotator, a first port, a second port, a third port, and afourth port. The optical source produces an optical signal. The firstpolarization splitter-rotator generates a first source optical signalbased at least in part on the optical signal. The second polarizationsplitter-rotator generates a second source optical signal based at leastin part on the optical signal. The first port transmits, to a firstdevice, the first source optical signal and receives, from the firstdevice, a first modulated optical signal. The first modulated opticalsignal has a polarization that is orthogonal to a polarization of thefirst source optical signal. The first polarization splitter-rotatorproduces a second modulated optical signal based at least in part on thefirst modulated optical signal. The second port transmits, to a seconddevice, the second source optical signal and receives, from the seconddevice, a third modulated optical signal. The third modulated opticalsignal has a polarization that is orthogonal to a polarization of thesecond source optical signal. The second polarization splitter-rotatorproduces a fourth modulated optical signal based at least in part on thethird modulated optical signal. The third port transmits the secondmodulated optical signal to the second device. The fourth port transmitsthe fourth modulated optical signal to the first device.

According to another embodiment, a method includes producing, by anoptical source, an optical signal and generating, by a firstpolarization splitter-rotator, a first source optical signal based atleast in part on the optical signal. The method also includesgenerating, by a second polarization splitter-rotator, a second sourceoptical signal based at least in part on the optical signal andtransmitting, by a first port and to a first device, the first sourceoptical signal. The method further includes receiving, by the first portand from the first device, a first modulated optical signal. The firstmodulated optical signal has a polarization that is orthogonal to apolarization of the first source optical signal. The method alsoincludes producing, by the first polarization splitter-rotator, a secondmodulated optical signal based at least in part on the first modulatedoptical signal and transmitting, by a second port and to a seconddevice, the second source optical signal. The method further includesreceiving, by the second port and from the second device, a thirdmodulated optical signal having a polarization that is orthogonal to apolarization of the second source optical signal and producing, by thesecond polarization splitter-rotator, a fourth modulated optical signalbased at least in part on the third modulated optical signal. The methodalso includes transmitting, by a third port, the second modulatedoptical signal to the second device and transmitting, by a fourth port,the fourth modulated optical signal to the first device.

According to another embodiment, a system includes a source device, areceiver device, and a pluggable device attached to the source device.The pluggable devices includes an optical module includes an opticalsource, a first polarization splitter-rotator, a second polarizationsplitter-rotator, a first port, a second port, a third port, and afourth port. The optical source produces an optical signal. The firstpolarization splitter-rotator generates a first source optical signalbased at least in part on the optical signal. The second polarizationsplitter-rotator generates a second source optical signal based at leastin part on the optical signal. The first port transmits, to the receiverdevice, the first source optical signal and receives, from the receiverdevice, a first modulated optical signal. The first modulated opticalsignal has a polarization that is orthogonal to a polarization of thefirst source optical signal. The first polarization splitter-rotatorproduces a second modulated optical signal based at least in part on thefirst modulated optical signal. The second port transmits, to the sourcedevice, the second source optical signal and receives, from the sourcedevice, a third modulated optical signal. The third modulated opticalsignal has a polarization that is orthogonal to a polarization of thesecond source optical signal. The second polarization splitter-rotatorproduces a fourth modulated optical signal based at least in part on thethird modulated optical signal. The third port transmits the secondmodulated optical signal to the source device. The fourth port transmitsthe fourth modulated optical signal to the receiver device.

EXAMPLE EMBODIMENTS

The present disclosure describes systems and methods for opticalcommunication that use laserless optical transceivers. Generally, theseoptical transceivers do not have their own optical sources (e.g., laserdiodes). Rather, they use source optical signals from other devices(e.g., other optical devices). For example, these optical transceiversmay include a reflective modulator that receives a source optical signalfrom another optical device. The reflective modulator modulates thatsource optical signal using a data signal to produce a modulated opticalsignal. The transceiver then communicates the modulated signal back tothe other optical device. The other optical device may include apolarization splitter-rotator and a transimpedance amplifier or aphotodiode that allows the data to be recovered from the modulatedsignal. In this manner, the optical transceiver does not include its ownoptical source, which reduces heat generation or heat sensitivity withinthe optical transceiver.

In some embodiments, the optical source may be provided in a pluggabledevice that connects to multiple devices. The pluggable device mayinclude multiple polarization splitter-rotators that produce sourceoptical signals for the multiple, connected devices. Reflectivemodulators at the connected devices modulate the source optical signalsusing data signals to produce modulated optical signals. The connecteddevices communicate the modulated signals back to the pluggable device.The pluggable device then reflects the modulated signals to otherconnected devices. In this manner, none of the connected devices mayhave their own optical sources. Rather, the pluggable device providesthe optical source for the connected devices, which reduces the heatgeneration or heat sensitivity in the connected devices.

FIG. 1 illustrates an example optical system 100. As seen in FIG. 1 ,the optical system 100 includes a source device 102 and a receiverdevice 104. Generally, the source device 102 and the receiver device 104are optical transceivers that transmit and receive optical signals overan optical link 106 that connects the source device 102 and the receiverdevice 104. The source device 102 and the receiver device 104 mayconvert received optical signals into electrical signals. The sourcedevice 102 and the receiver device 104 may then communicate theelectrical signals to other devices, such as computers or servers, foranalysis and processing. The source device 102 and receiver device 104may receive electrical signals and convert those received electricalsignals into optical signals. The source device 102 and receiver device104 may then transmit those optical signals over the link 106 to theother device.

The source device 102 and the receiver device 104 may use a sourceoptical signal (e.g., a laser) to convert an electric signal into anoptical signal. For example, the source device 102 or the receiverdevice 104 may modulate the source optical signal using the electricalsignal to convert the electrical signal into the optical signal. Thesource optical signal may be produced by an optical source (e.g., alaser diode). The optical sources, however, occupy physical space andgenerate heat, which may interfere with the operations of certaincomponents within the source device 102 or the receiver device 104. Insome embodiments, to reduce the amount of generated heat and the amountof space occupied by optical sources in the optical system 100, one ormore of the components within the optical system 100 may not include anoptical source. For example, the receiver device 104 may not include anoptical source. Rather, the receiver device 104 may receive a sourceoptical signal from the source device 102 over the link 106. The sourcedevice 102 and the receiver device 104 may include components thatoperate on the source optical signal so that the source optical signaland a modulated optical signal may be communicated over the link 106.

The link 106 may include one or more optical fibers that communicateoptical signals between the source device 102 and the receiver device104. In some embodiments, the link 106 includes two single mode fibersthat communicate optical signals between the source device 102 and thereceiver device 104. One of the single mode fibers may be used tocommunicate a modulated optical signal from the source device 102 to thereceiver device 104. The other single mode fiber may be used tocommunicate the source optical signal from the source device 102 to thereceiver device 104 and a modulated optical signal from the receiverdevice 104 to the source device 102.

The optical system 100 may include any suitable number of source devices102, receiver devices 104, and links 106. In one embodiment, the opticalsystem 100 includes multiple receiver devices 104. The source device 102connects to each of the receiver devices 104 using multiple links 106that connect the source device 102 to the receiver devices 104. Thesource device 102 may provide a source optical signal to each of thereceiver devices 104 over the links 106.

FIG. 2 illustrates example components of the optical system 100 of FIG.1 . As seen in FIG. 2 , the optical system 100 includes the sourcedevice 102 and the receiver device 104. Generally, the source device 102and the receiver device 104 are optical transceivers that communicatemodulated optical signals to each other. Additionally, the source device102 provides a source optical signal to the receiver device 104. Thesource device 102 and the receiver device 104 include components thatallow the source optical signal to be communicated over the same fiberas a modulated optical signal.

The source device 102 communicates a modulated optical signal to thereceiver device 104 and a source optical signal to the receiver device104. As seen in FIG. 2 , the source device 102 includes an opticalsource 202, a modulator 204, a polarization splitter-rotator 206, asignal processor 208, and a transimpedance amplifier or photodiode 210.These components operate together to communicate a modulated opticalsignal to the receiver device 104 over a first optical fiber 218 and asource optical signal to the receiver device 104 over a second opticalfiber 220. Each of these optical fibers 218 and 220 may be single modefibers. In certain embodiments, using single mode fibers simplifies theoptical coupling and reduces costs relative to using multimode fibers.

The optical source 202 is a component that emits an optical signal. Forexample, the optical source 202 may be a laser diode that emits a laser.The laser may be used by the source device 102 to produce a sourceoptical signal for the receiver device 104. The optical source 202 maybe disposed within the source device 102. In some embodiments, theoptical source 202 may be disposed in another device rather than thesource device 102 and the receiver device 104. The optical source 202may emit an optical signal that is directed to the source device 102.The source device 102 may use the optical signal to produce a sourceoptical signal for the receiver device 104. As seen in FIG. 2 , theoptical source 202 emits an optical signal that is directed to themodulator 204 and the polarization splitter-rotator 206.

The modulator 204 modulates the optical signal from the optical source202 using a data signal from the signal processor 208 to produce amodulated optical signal. The signal processor 208 may have received thedata used to form the data signal from an external source (e.g., acomputer or server). In some embodiments, the modulator 204 is a PAM4modulator that performs PAM4 encoding on the optical signal from theoptical source 202 using the data signal. The data signal is an electricsignal that represents data from the signal processor 208. The modulator204 effectively encodes the electric data signal into the optical signalfrom the optical source 202 to produce the modulated optical signal. Asa result, the modulated optical signal is an optical signal thateffectively includes information from the data signal. The modulator 204directs the modulated optical signal to the receiver device 104 over theoptical fiber 218 of the optical link between the source device 102 andthe receiver device 104. In some embodiments, the optical fiber 218 is asingle mode fiber.

The polarization splitter-rotator 206 rotates the polarization ofincoming optical signals and then combines or splits the opticalsignals. As seen in FIG. 2 , the polarization splitter-rotator 206receives the optical signal from the optical source 202. Thepolarization splitter-rotator 206 rotates the polarization of theoptical signal to produce a source optical signal. The polarizationsplitter-rotator 206 then directs the source optical signal to thereceiver device 104 over the optical fiber 220 of the optical linkbetween the source device 102 and the receiver device 104.

The polarization splitter-rotator 206 also receives a modulated opticalsignal from the receiver device 104 over the same optical fiber 220 thatis used to communicate the source optical signal from the source device102 to the receiver device 104. The modulated optical signal from thereceiver device 104 may have a polarization that is orthogonal to thepolarization of the source optical signal from the source device 102. Asa result, the source optical signal and the modulated optical signal maybe communicated over the same fiber 220. The polarizationsplitter-rotator 206 receives the modulated optical signal from thereceiver device 104 and rotates the polarization of the modulatedoptical signal. After rotating the polarization of the modulated opticalsignal, the polarization splitter-rotator 206 directs the modulatedoptical signal to the transimpedance amplifier or photodiode 210.

The polarization splitter-rotator 206, as shown herein, may include anysuitable components that rotate the polarization of optical signals andthen combines or splits the optical signals. For example, thepolarization splitter-rotator 206 may include polarization splittergrading couplers, polarization beam splitters with a quarter wave plate,or integrated photonics that perform the same function.

The transimpedance amplifier or photodiode 210 detects the modulatedoptical signal from the polarization splitter-rotator 206 and convertsthe modulated optical signal into an electrical signal. Specifically,the transimpedance amplifier or the photodiode 210 may detect themodulated optical signal and produce an electrical signal representingthe modulated optical signal. The transimpedance amplifier or thephotodiode 210 directs the electrical signal to the signal processor208. The signal processor 208 processes the electrical signal todetermine data encoded within the electrical signal. The signalprocessor 208 may then communicate that data to another device (e.g., acomputer or a server).

The receiver device 104 includes a transimpedance amplifier orphotodiode 212 that receives the modulated optical signal from thesource device 102 over the fiber 218. The transimpedance amplifier orphotodiode 212 converts the modulated optical signal into an electricalsignal. For example, the transimpedance amplifier or the photodiode 212may detect the modulated optical signal and produce an electrical signalrepresenting the modulated optical signal. The transimpedance amplifieror photodiode 212 communicate the electrical signal to a signalprocessor 214 in the receiver device 104. The signal processor 214processes the electrical signal to determine data encoded within theelectrical signal. The signal processor 214 then communicates that datato another device (e.g., a computer or a server).

The signal processor 214 may receive data from the other device. Thedata may be in response to the data that the signal processor 214communicated to that device. The signal processor 214 may process thatdata and encode that data within a data signal. The data signal may beanother electrical signal. The signal processor 214 communicates thatdata signal to a reflective modulator 216 in the receiver device 104.

The reflective modulator 216 receives the data signal from the signalprocessor 214 and the source optical signal from the source device 102.The reflective modulator 216 modulates the source optical signal usingthe data signal to produce a modulated optical signal. In certainembodiments, the reflective modulator 216 modulates the source opticalsignal in such a manner that the modulated optical signal has apolarization that is orthogonal to the polarization of the sourceoptical signal. For example, the reflective modulator 216 may modulatethe source optical signal using the data signal to produce the modulatedoptical signal with a polarization that is 90 degrees rotated from thepolarization of the source optical signal. Because the polarization ofthe source optical signal is orthogonal to the polarization of themodulated optical signal, the source optical signal and the modulatedoptical signal may be communicated over the same fiber 220, which may bea single mode fiber. The reflective modulator 216 directs the modulatedoptical signal to the source device 102 over the same fiber 220 thatdirected the source optical signal to the reflective modulator 216. Inthis manner, the receiver device 104 modulates the source optical signalfrom the source device 102 and communicates the modulated opticalsignals over the same fiber 220 that provided the source optical signal.As a result, the receiver device 104 does not include a separate opticalsource that provides a source optical signal, which reduces the heatgeneration of the receiver device 104, in certain embodiments.

The reflective modulators described herein may be any suitablereflective modulator. For example, the reflective modulators may beFaraday-rotator-based reflective modulators,polarization-splitter-rotator-based reflective modulators, reflectivemodulators with bulk polarization beam splitters with polarizationrotation, or vertically coupled reflective modulators.

The signal processors 208 and 214 may be any electronic circuitry,including, but not limited to one or a combination of microprocessors,microcontrollers, application specific integrated circuits (ASIC),application specific instruction set processor (ASIP), and/or statemachines, that execute software or firmware to control the operation ofthe source device 102 and the receiver device 104. The signal processors208 and 214 may be 8-bit, 16-bit, 32-bit, 64-bit or of any othersuitable architecture. The signal processors 208 and 214 may include anarithmetic logic unit (ALU) for performing arithmetic and logicoperations, processor registers that supply operands to the ALU andstore the results of ALU operations, and a control unit that fetchesinstructions from memory and executes them by directing the coordinatedoperations of the ALU, registers and other components. The signalprocessors 208 and 214 may include other hardware that operates softwareto control and process information. The signal processors 208 and 214control the operation and administration of the source device 102 andreceiver device 104 by processing information (e.g., informationreceived from the source device 102 and the receiver device 104). Thesignal processors 208 and 214 are not limited to single processingdevices and may encompass multiple processing devices.

FIG. 3 illustrates example components of the optical system 100 of FIG.1 . Generally, the example of FIG. 3 shows the source device 102 usingmultiple optical sources 202 to produce multiple optical signals thatare modulated using multiple data signals. The source device 102 and thereceiver device 104 are optical transceivers that may includemultiplexers and de-multiplexers that combine and separate thesemultiple optical signals or modulated optical signals.

The source device 102 includes multiple optical sources 202. Each of theoptical sources 202 may be a laser diode that produces or emits anoptical signal. For example, each optical source 202 may emit an opticalsignal with a different wavelength. These optical signals may then bemodulated using multiple data signals.

The source device 102 includes multiple modulators 204 that modulatedifferent optical signals from the optical sources 202 using datasignals from the signal processor 208. The signal processor 208 may havereceived data from an external device (e.g., a computer or server). Thesignal processor 208 may process this data and encode the data into thedata signals. The data signals may then be provided to the modulators204 for modulation. Each modulator 204 may receive a different datasignal from the signal processor 208 for modulation. Additionally, eachmodulator 204 may receive an optical signal from a different opticalsource 202. As a result, in some embodiments, each modulator 204 mayreceive an optical signal with a different wavelength. The modulators204 modulate the optical signals from the optical sources 202 using thedata signals to produce multiple modulated optical signals.

The modulators 204 direct the modulated optical signals to a multiplexer302. The multiplexer 302 may perform wavelength division multiplexing tocombine the modulated optical signals from the modulators 204 into asingle-beam. The multiplexer 302 then communicates the single-beammodulated optical signal to the receiver device 104 over a fiber 218 ofthe optical link between the source device 102 and the receiver device104. This fiber 218 may be a single mode fiber.

The source device 102 includes a multiplexer 304 that receives theoptical signals from the optical sources 202. In certain embodiments,the multiplexer 304 performs wavelength division multiplexing on theoptical signals from the optical sources 202 to combine the opticalsignals into a single beam. The multiplexer 304 directs the single beamto the polarization splitter-rotator 206. As discussed previously, thepolarization splitter-rotator 206 rotates the polarization of the beamto produce a source optical signal and communicates the source opticalsignal to the receiver device 104 over the fiber 220.

The polarization splitter-rotator 206 receives a modulated opticalsignal from the receiver device 104. As discussed previously, themodulated optical signal may have a polarization that is orthogonal tothe polarization of the source optical signal. As a result, the sourceoptical signal and the modulated optical signal may be communicatedbetween the source device 102 and the receiver device 104 over the samefiber 220. The polarization splitter-rotator 206 rotates thepolarization of the modulated optical signal and then directs themodulated optical signal to a de-multiplexer 306 of the source device102. In certain embodiments, the de-multiplexer 306 de-multiplexes themodulated optical signal to split the modulated optical signal intomultiple modulated optical signals. The source device 102 includesmultiple transimpedance amplifiers or photodiodes 210 that convert themultiple modulated optical signals from the de-multiplexer 306 intomultiple electrical signals. The transimpedance amplifiers orphotodiodes 210 direct the electrical signals to the signal processor208. The signal processor 208 processes these electrical signals toextract data encoded within these electrical signals. The signalprocessor 208 then communicates that data out to external devices (e.g.,computers or servers).

The receiver device 104 also includes multiplexers and de-multiplexers,that allow the receiver device 104 to handle multiple optical signalsgenerated from different optical signals. The receiver device 104includes a de-multiplexer 308 that receives the modulated optical signalfrom the source device 102 over the fiber 218. As discussed previously,the modulated optical signal may have been produced by combiningmultiple modulated optical signals at the multiplexer 302 of the sourcedevice 102. The de-multiplexer 308 de-multiplexes the modulated opticalsignal to split the single-beam modulated optical signal into themultiple modulated optical signals that were combined at the multiplexer302. The de-multiplexer 308 directs the multiple modulated opticalsignals to multiple transimpedance amplifiers or photodiodes 212 in thereceiver device 104. The transimpedance amplifiers or photodiodes 212convert the multiple modulated optical signals into multiple electricalsignals. The transimpedance amplifiers or photodiodes 212 direct themultiple electrical signals to the signal processor 214. The signalprocessor 214 processes the electrical signals and extracts data encodedwithin the electrical signals. The signal processor 214 thencommunicates the data to external devices such as computers or servers.

The signal processor 214 may receive data from the external devices. Thesignal processor 214 processes the received data and encodes the datainto multiple data signals. The signals processor 214 then directs themultiple data signals to multiple reflective modulators 216 in thereceiver device 104.

As discussed previously, the reflective modulators 216 modulate thesource optical signals received from the source device 102 using thedata signals received from the signal processor 214 such that theresultant modulated optical signals have a polarization that isorthogonal to the polarization of the source optical signals used toproduce the modulated optical signals. In the example of FIG. 3 , thereceiver device 104 includes a polarization splitter-rotator 310 thatreceives the single-beam source optical signal from the source device102. The polarization splitter-rotator 310 rotates the polarization ofthe single beam source optical signal. In some embodiments, thepolarization splitter-rotator 310 rotates the polarization of the singlebeam source optical signal to reverse the polarization rotationperformed by the polarization splitter-rotator 206 of the source device102. After rotating the polarization of the single beam source opticalsignal from the source device 102, the polarization splitter-rotator 310directs the source optical signal to a multiplexer de-multiplexer 312.The multiplexer de-multiplexer 312 de-multiplexes the source opticalsignal to produce multiple source optical signals. In some embodiments,the multiplexer de-multiplexer 312 performs wavelength divisionmultiplexing to split the single-beam source optical signal intomultiple source optical signals of different wavelengths. Themultiplexer de-multiplexer 312 then directs the multiple source opticalsignals to the multiple reflective modulators 216.

Each reflective modulator 216 then modulates a source optical signalwith a different wavelength using their respective data signals toproduce a modulated optical signal. The reflective modulators 216communicate their respective modulated optical signals to themultiplexer de-multiplexer 312. The multiplexer de-multiplexer 312 thenperforms wavelength division multiplexing on the multiple modulatedoptical signals to combine the multiple modulated optical signals into asingle beam. The multiplexer de-multiplexer 312 then directs thesingle-beam modulated optical signal to the polarizationsplitter-rotator 310. The polarization splitter-rotator 310 rotates thepolarization of the single-beam modulated optical signal andcommunicates the single-beam modulated optical signal back to the sourcedevice 102 over the fiber 220. As discussed previously, the polarizationof the single-beam modulated optical signal may be orthogonal to thepolarization of the single-beam source optical signal. As a result, thesingle-beam source optical signal and the single-beam modulated opticalsignal may be communicated between the source device 102 and thereceiver device 104 using the same optical fiber 220, which may be asingle mode fiber. The source device 102 may split the single-beammodulated optical signal and convert the multiple modulated opticalsignals into electrical signals for processing.

FIG. 4 illustrates an example optical system 400. As seen in FIG. 4 ,the optical system 400 includes a source device 102 and multiplereceiver devices 104. Generally, the source device 102 includes multiplemodulators 204, multiple polarization splitter-rotators 206, andmultiple transimpedance amplifiers or photodiodes 210, which operate toproduce source optical signals and modulated optical signals for themultiple receiver devices 104. The source device 102 may include amodulator 204 for each receiver device 104, a polarizationsplitter-rotator 206 for each receiver device 104, and a transimpedanceamplifier or photodiode 210 for each receiver device 104.

The optical source 202 provides an optical signal to each of themodulators 204. Additionally, the signal processor 208 provides a datasignal to each of the modulators 204. Although the optical signalsprovided to the modulators 204 may be the same, the data signalsprovided by the signal processor 208 to each of the modulators 204 maynot be the same, as each data signal may be intended for a differentreceiver device 104. The modulators 204 modulate the optical signal fromthe optical source 202 using the data signals from the signal processor208 to produce modulated optical signals. Each modulator 204communicates their respective modulated optical signal to a differentreceiver device 104. For clarity, communication between the sourcedevice 102 and only one receiver device 104 is shown in FIG. 4 .

The source device 102 also includes a polarization splitter-rotator 206for each receiver device 104. Each polarization splitter-rotator 206receives an optical signal from the optical source 202. Eachpolarization splitter-rotator 206 rotates the polarization of theoptical signal to produce a source optical signal. Each polarizationsplitter-rotator 206 then directs their respective source optical signalto a different receiver device 104.

Each receiver device 104 includes a transimpedance amplifier orphotodiode 212 that receives the modulated optical signal from thesource device 102. The transimpedance amplifier or photodiode 212converts the modulated optical signal into an electrical signal, whichis then processed by the signal processor 214. The signal processor 214may extract data encoded within the electrical signal and communicatethat data to a computer or server. The signal processor 214 may receivedata from the computer or server and encode that data into a datasignal.

Each receiver device 104 includes a reflective modulator 216 thatreceives a source optical signal from the source device 102 and a datasignal from the respective signal processor 214 of the receiver device104. The reflective modulator 216 modulates the source optical signalfrom the source device 102 using the data signal to produce a modulatedoptical signal. The reflective modulator 216 modulates the opticalsignal in such a manner that the modulated optical signal has apolarization that is orthogonal to the polarization of the sourceoptical signal. For example, the polarization of the modulated opticalsignal may be different from the polarization of the source opticalsignal by 90 degrees. Because the polarization of the modulated opticalsignal is orthogonal to the polarization of the source optical signal,the reflective modulator 216 may communicate the modulated opticalsignal back to the source device 102 over the same fiber 220 that wasused for the source optical signal.

Each polarization splitter-rotator 206 in the source device 102 mayreceive a modulated optical signal from a different receiver device 104.The polarization splitter-rotators 206 rotate the polarization of thereceived modulated optical signals and communicate those modulatedoptical signals to the transimpedance amplifiers or photodiodes 210.Each transimpedance amplifier or photodiode 210 converts a modulatedoptical signal into an electrical signal. The transimpedance amplifiersor photodiodes 210 communicate the electrical signals to the signalprocessor 208. The signal processor 208 processes the electrical signalsto extract data encoded within the electrical signals. The signalprocessor 208 then communicates that data to external computers orservers.

FIG. 5 is a flowchart of an example method 500 performed in the opticalsystems 100 or 400 of FIGS. 1 and 4 . In certain embodiments, the sourcedevice 102 and the receiver device 104 perform the steps of the method500. By performing the method 500, the source device 102 provides asource optical signal for the receiver device 104, such that thereceiver device 104 may not include a separate optical source.

In step 502, the source device 102 generates a source optical signal.The source device 102 includes an optical source 202 (e.g., a laserdiode) that emits an optical signal. The source device 102 includes apolarization splitter-rotator 206 that receive the optical signal fromthe optical source 202. The polarization splitter-rotator 206 rotatesthe polarization of the optical signal to produce the source opticalsignal. The polarization splitter-rotator 206 then communicates thesource optical signal to the receiver device 104 over an optical fiber220 of the optical link 106 between the source device 102 and thereceiver device 104. In some embodiments, the optical fiber 220 is asingle mode fiber.

In step 504, the receiver device 104 modulates the source optical signalprovided by the source device 102 using a data signal. The receiverdevice 104 includes the reflective modulator 216 that modulates thesource optical signal from the source device 102 using the data signalfrom the signal processor 214. In some embodiments, the reflectivemodulator 216 modulates the optical signal in such a manner that theresultant modulated optical signal has a polarization that is orthogonalto the polarization of the source optical signal from the source device102. For example, the polarization of the modulated optical signal maybe different from the polarization of the source optical signal by 90degrees. As discussed previously, because the polarization of themodulated optical signal is orthogonal to the polarization of the sourceoptical signal, the receiver device 104 may communicate the modulatedoptical signal back to the source device 102 using the same fiber 220that was used to communicate the source optical signal from the sourcedevice 102 to the receiver device 104. The reflective modulator 216communicates the modulated optical signal back to the source device 102using this optical fiber 220, which may be a single mode fiber.

In step 506, the source device 102 recovers the data signal from themodulated optical signal. The polarization splitter-rotator 206 receivesthe modulated optical signal from the receiver device 104 and rotatesthe polarization of the modulated optical signal. The polarizationsplitter-rotator 206 then communicates the modulated optical signal tothe transimpedance amplifier or photodiode 210. The transimpedanceamplifier or photodiode 210 converts the modulated optical signal intoan electrical signal. The transimpedance amplifier or photodiode 210then communicates the electrical signal to the signal processor 208 inthe source device 102. The signal processor 208 processes the electricalsignal to extract the data encoded within the electrical signal andcommunicates that data to an external computer or server.

In some embodiments, the source optical signal for the optical system isprovided by a pluggable device. The pluggable device includes an opticalsource that produces optical signals. The pluggable device may includeother components (e.g., polarization splitter-rotators, isolators, andlenses) that use the optical signals from the optical source to producesource optical signals. The pluggable device directs the source opticalsignals to the devices in the optical system (e.g., the source deviceand the receiver device). Additionally, the pluggable device may receivemodulated optical signals from the source device and the receiverdevice. The pluggable device may direct the modulated optical signals tothe receiver device and the source device. In this manner, the pluggabledevice provides source optical signals to the source device and thereceiver device, and relays modulated optical signals between the sourcedevice and the receiver device.

The pluggable device may also form a physical connection with the sourcedevice, in addition to an optical connection. For example, the pluggabledevice may plug into the source device and be held in place by physicalconnectors (e.g., latches or tabs).

FIG. 6 illustrates an example optical system 600. As seen in FIG. 6 ,the optical system 600 includes the source device 102 and the receiverdevice 104, which may be optical transceivers. An optical link 106connects the source device 102 and the receiver device 104. The opticalsystem 600 also includes a pluggable device 602 that is plugged into thesource device 102. The pluggable device 602 may produce source opticalsignals for the source device 102 and the receiver device 104. Thesource device 102 and the receiver device 104 may use the source opticalsignals to produce modulated optical signals. The pluggable device 602relays the modulated optical signals between the source device 102 andthe receiver device 104.

The pluggable device 602 may interface with the receiver device 104through the optical link 106. For example, the pluggable device 602 mayprovide a source optical signal to the receiver device 104 through theoptical link 106. Additionally, the pluggable device 602 may transmitmodulated optical signals to the receiver device 104 and receivemodulated optical signals from the receiver device 104 over the opticallink 106. In some embodiments, the optical link 106 may include twosingle mode fibers. The pluggable device 602 may transmit modulatedoptical signals to the receiver device 104 over one of the single modefibers, and the pluggable device 602 may transmit a source opticalsignal to the receiver device 104 over the other single mode fiber.Additionally, the pluggable device 602 may receive modulated opticalsignals from the receiver device 104 over the same single mode fiberused to transmit the source optical signal to the receiver device 104.The received modulated optical signal may have a polarization that isorthogonal to the polarization of the source optical signal.

FIG. 7 illustrates an example pluggable device 602 in the optical system600 of FIG. 6 . As discussed previously, the pluggable device 602 mayplug into the source device 102 and provide source optical signals tothe source device 102 and the receiver device 104 in the optical system600 of FIG. 6 . As seen in FIG. 7 , the pluggable device 602 includes anoptical source 202 that produces optical signals. The optical source 202may be a laser diode that emits lasers. The pluggable device 602includes other components that produce any suitable number of sourceoptical signals from the optical signals emitted by the optical source202.

In the example of FIG. 7 , the pluggable device 602 produces two sourceoptical signals from the optical signals produced by the optical source202. Each side of the pluggable device 602 includes components that usean optical signal produced by the optical source 202 to produce a sourceoptical signal. As seen in FIG. 7 , the pluggable device 602 includestwo polarization splitter-rotators 206 that use an optical signal fromthe optical source 202 to produce a source optical signal. As discussedpreviously, each polarization splitter-rotator 206 rotates thepolarization of the optical signal from the optical source 202 toproduce the source optical signal. Each polarization splitter-rotator206 directs their corresponding source optical signal to a port. In theexample of FIG. 7 , a polarization splitter-rotator 206 directs itssource optical signal to a port 704, and a polarization splitter-rotator206 directs its source optical signal to a port 708. The port 704 maydirect the source optical signal to the source device 102, and the port708 may direct the source optical signal to the receiver device 104.

In certain embodiments, the pluggable device 602 includes an opticalisolator 712 for each polarization splitter-rotator 206. Each opticalisolator 712 may receive an optical signal from the optical source 202and force the optical signal to propagate in a particular direction. Forexample, each optical isolator 712 may direct an optical signal from theoptical source 202 to a polarization splitter-rotator 206 in thepluggable device 602. In some embodiments, Faraday rotators are usedinstead of optical isolators 712 in the pluggable device 602. TheFaraday rotators also force a received optical signal to propagate in aparticular direction.

The source device 102 and the receiver device 104 may include reflectivemodulators that produce a modulated optical signal using a data signaland the source optical signal provided by the pluggable device 602.These reflective modulators may produce modulated optical signals thathave a polarization that is orthogonal to the polarization of the sourceoptical signals. As a result, the modulated optical signals may becommunicated back to the pluggable device 602 over the same opticalfiber that was used to communicate the source optical signals to thesource device 102 and the receiver device 104. As seen in FIG. 7 , thepluggable device 602 receives modulated optical signals at the ports 704and 708 that were used to communicate the source optical signals awayfrom the pluggable device 602. These modulated optical signals may bereceived over the same fibers that were used to communicate the sourceoptical signals away from the pluggable device 602. The ports 704 and708 direct the modulated optical signals to the polarizationsplitter-rotators 206. The polarization splitter-rotators 206 rotate thepolarization of the modulated optical signals and then direct themodulated optical signals to mirrors 714.

The mirrors 714 reflect the modulated optical signals from thepolarization splitter-rotators 206 to other ports 702 and 706 of thepluggable device 602. The port 702 may direct the modulated opticalsignal to the receiver device 104, and the port 706 may direct themodulated optical signal to the source device 102. In some embodiments,the port 702 interfaces with the receiver device 104 over an opticalfiber separate from the optical fiber used to communicate the sourceoptical signal to the receiver device 104. Additionally, the port 706interfaces with the source device 102 using an optical fiber separatefrom the optical fiber used to the communicate the source optical signalto the source device 102.

In some embodiments, the pluggable device 602 includes lenses 710 thatdirect various signals to components within the pluggable device 602. Asseen in FIG. 7 , the pluggable device 602 includes a lens 710 betweenthe optical source 202 and the isolator 712. Additionally, the pluggabledevice 602 includes a lens 710 between the port 704 and the polarizationsplitter-rotator 206. Another lens 710 is included between the port 708and the polarization splitter-rotator 206. Lenses 710 are also includedbetween the mirror 714 and the port 706 and the mirror 714 and the port702. Each of the lenses 710 directs the various optical signals in thepluggable device 602 to other components in the pluggable device 602(e.g., ports 702, 704, 706, and 708, polarization splitter-rotators 206,and isolators 712).

FIG. 8 illustrates example components of the optical system 600 of FIG.6 . As seen in FIG. 8 , the pluggable device 602 connects through theports 702, 704, 706, and 708 to the source device 102 and the receiverdevice 104. Specifically, the pluggable device 602 connects to thesource device 102 through the ports 704 and 706, and the pluggabledevice 602 connects to the receiver device 104 through the ports 702 and708. The pluggable device 602 may form other physical connections withthe source device 102 (e.g., a pluggable interface of the source device102).

The source device 102 includes a transimpedance amplifier or photodiode802 and a reflective modulator 804. The transimpedance amplifier orphotodiode 802 receives a modulated optical signal from the port 706 ofthe pluggable device 602 over a fiber 810, which may be a single modefiber. As discussed previously, the modulated optical signal may havebeen communicated to the pluggable device 602 from the receiver device104 through the port 708. The transimpedance amplifier or photodiode 802detects the modulated optical signal and converts the modulated opticalsignal into an electrical signal.

The reflective modulator 804 receives the source optical signal from theport 704 of the pluggable device 602 over the fiber 814. The reflectivemodulator 804 modulates the source optical signal using a data signal toproduce a modulated optical signal. The reflective modulator 804modulates the optical signal such that the produced modulated opticalsignal has a polarization that is orthogonal to the polarization of thesource optical signal. For example, the modulated optical signal mayhave a polarization that is different from the polarization of thesource optical signal by 90 degrees. Because the modulated opticalsignal has a polarization that is orthogonal to the polarization of thesource optical signal, the modulated optical signal may be communicatedover the same optical fiber 814 as the source optical signal. As aresult, the reflective modulator 804 may communicate the producedmodulated optical signal back to the port 704 over the same fiber 814that was used to communicate the source optical signal to the reflectivemodulator 804. The fiber 814 may be a single mode fiber.

The receiver device 104 includes a transimpedance amplifier orphotodiode 806 and a reflective modulator 808. The transimpedanceamplifier or photodiode 806 receives a modulated optical signal from theport 702 of the pluggable device 602 over the fiber 812, which may be asingle mode fiber. The modulated optical signal may have beencommunicated to the pluggable device 602 from the source device 102through the port 704. The transimpedance amplifier or photodiode 806detects the modulated optical signal and converts the modulated opticalsignal into an electrical signal.

The reflective modulator 808 receives a source optical signal from theport 708 of the pluggable device 602 over the fiber 816. The reflectivemodulator 808 modulates the source optical signal using a data signal toproduce a modulated optical signal. The reflective modulator 808 maymodulate the optical signal such that the produced modulated opticalsignal has a polarization that is orthogonal to the polarization of thesource optical signal. For example, the produced modulated opticalsignal may have a polarization that is different from the polarizationof the source optical signal by 90 degrees. Because the polarization ofthe modulated optical signal is orthogonal to the polarization of thesource optical signal, the modulated optical signal may be communicatedover the same fiber 816 as the source optical signal. As a result, thereflective modulator 808 may communicate the produced modulated opticalsignal back to the port 708 using the same fiber 816 that was used tocommunicate the source optical signal to the receiver device 104.

FIG. 9 is a flowchart of an example method 900 performed in the opticalsystem 600 of FIG. 6 . Various components of the optical system 600perform the method 900. In particular embodiments, by performing themethod 900, the pluggable device 602 may be used to provide sourceoptical signals to the source device 102 and the receiver device 104.

In step 902, the optical source 202 of the pluggable device 602 producesan optical signal. The optical source 202 may be a laser diode thatemits a laser that acts as the optical signal. Other components of thepluggable device 602 may use the optical signal to produce sourceoptical signals for the source device 102 and the receiver device 104.

In step 904, a polarization splitter-rotator 206 generates a firstsource optical signal using an optical signal from the optical source202. The polarization splitter-rotator 206 may direct the first sourceoptical signal to a port 704 that interfaces with the source device 102over a fiber 814. In step 906, another polarization splitter-rotator 206generates a second source optical signal using an optical signalproduced by the optical source 202. This polarization splitter-rotator206 may direct the source optical signal to the port 708 that interfaceswith the receiver device 104 over a fiber 816.

In step 908, the pluggable device 602 transmits the first optical signalto the source device 102 through the port 704. The first source opticalsignal may be communicated to the source device 102 by the fiber 814,which may be a single mode fiber. The source device 102 includes thereflective modulator 804 that uses a data signal to modulate the sourceoptical signal to produce a first modulated optical signal. The firstmodulated optical signal may have a polarization that is orthogonal tothe polarization of the source optical signal. The source device 102communicates the first modulated optical signal over the same fiber 814that was used to communicate the source optical signal to the sourcedevice 102 and back to the port 704 of the pluggable device 602. In step910, the pluggable device 602 receives the first modulated opticalsignal at the port 704.

In step 912, the pluggable device 602 produces a second modulatedoptical signal. The first modulated optical signal may be received at apolarization splitter-rotator 206 of the pluggable device 602. This maybe the same polarization splitter-rotator 206 that produced the firstsource optical signal. The polarization splitter-rotator 206 rotates thepolarization of the first modulated optical signal to produce the secondmodulated optical signal. The polarization splitter-rotator 206 thendirects the second modulated optical signal to a mirror 714 thatreflects the second modulated optical signal to a port 702.

In step 914, the pluggable device 602 transmits the second sourceoptical signal to the receiver device 104. The pluggable device 602 maytransmit the second source optical signal through the port 708 to thereceiver device 104. The second source optical signal may becommunicated to the receiver device 104 over a fiber 816, which may be asingle mode fiber. The receiver device 104 includes the reflectivemodulator 808 that uses a data signal to modulate the second sourceoptical signal and to produce a third modulated optical signal. Thethird modulated optical signal may have a polarization that isorthogonal to the polarization of the second source optical signal. As aresult, the reflective modulator 808 communicates the third modulatedoptical signal back to the port 708 of the pluggable device 602 over thesame fiber 816 used to communicate the second source optical signal tothe receiver device 104. In step 916, the pluggable device 602 receivesthe third modulated optical signal at the port 708.

In step 918, the pluggable device 602 produces a fourth modulatedoptical signal. The polarization splitter-rotator 206 that produced thesecond source optical signal may receive the third modulated opticalsignal and rotate the polarization of the third modulated optical signalto produce the fourth modulated optical signal. The polarizationsplitter-rotator 206 then directs the fourth modulated optical signal toa mirror 714 that reflects the fourth modulated optical signal to theport 706.

In step 920, the pluggable device 602 transmits the second modulatedoptical signal to the receiver device 104 using the port 702 and thefiber 812. In step 922, the pluggable device 602 transmits the fourthmodulated optical signal to the source device 102 using the port 706 andthe fiber 810. In this manner, the pluggable device 602 allows thesource device 102 and the receiver device 104 to communicate modulatedoptical signals to each other.

In summary, an optical system includes a source device 102 and areceiver device 104. The receiver device 104 does not include an opticalsource. Rather, the source device 102 includes an optical source 202that provides a source optical signal to the receiver device 104. Thereceiver device 104 includes a reflective modulator 216 that receivesthe source optical signal from source device 102. The reflectivemodulator 216 modulates the source optical signal using a data signal toproduce a modulated optical signal. The receiver device 104 communicatesthe modulated optical signal back to the source device 102. The sourcedevice 102 includes a polarization splitter-rotator 206 and atransimpedance amplifier or a photodiode 210 that allow the data to berecovered from the modulated optical signal. In this manner, thereceiver device 104 does not include its own optical source, whichreduces heat generation within the receiver device 104.

In some embodiments, the optical source 202 may be provided in apluggable device 602 that connects to the source device 102 and thereceiver device 104. The pluggable device 602 may include multiplepolarization splitter-rotators 206 that produce source optical signalsfor the source device 102 and the receiver device 104. Reflectivemodulators 804 and 808 at the source device 102 and the receiver device104 modulate the source optical signals using data signals to producemodulated optical signals. The source device 102 and the receiver device104 communicate the modulated signals back to the pluggable device 602.The pluggable device 602 then reflects the modulated signals to thereceiver device 104 or the source device 102. In this manner, the sourcedevice 102 and the receiver device 104 may not have their own opticalsources 202. Rather, the pluggable device 602 provides the opticalsource 202 for the source device 102 and the receiver device 104, whichreduces the heat generation in the source device 102 and the receiverdevice 104.

In the current disclosure, reference is made to various embodiments.However, the scope of the present disclosure is not limited to specificdescribed embodiments. Instead, any combination of the describedfeatures and elements, whether related to different embodiments or not,is contemplated to implement and practice contemplated embodiments.Additionally, when elements of the embodiments are described in the formof “at least one of A and B,” or “at least one of A or B,” it will beunderstood that embodiments including element A exclusively, includingelement B exclusively, and including element A and B are eachcontemplated. Furthermore, although some embodiments disclosed hereinmay achieve advantages over other possible solutions or over the priorart, whether or not a particular advantage is achieved by a givenembodiment is not limiting of the scope of the present disclosure. Thus,the aspects, features, embodiments and advantages disclosed herein aremerely illustrative and are not considered elements or limitations ofthe appended claims except where explicitly recited in a claim(s).Likewise, reference to “the invention” shall not be construed as ageneralization of any inventive subject matter disclosed herein andshall not be considered to be an element or limitation of the appendedclaims except where explicitly recited in a claim(s).

As will be appreciated by one skilled in the art, the embodimentsdisclosed herein may be embodied as a system, method or computer programproduct. Accordingly, embodiments may take the form of an entirelyhardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,embodiments may take the form of a computer program product embodied inone or more computer readable medium(s) having computer readable programcode embodied thereon.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for embodiments of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatuses(systems), and computer program products according to embodimentspresented in this disclosure. It will be understood that each block ofthe flowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the block(s) of the flowchart illustrationsand/or block diagrams.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other device to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the block(s) of the flowchartillustrations and/or block diagrams.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other device to cause aseries of operational steps to be performed on the computer, otherprogrammable apparatus or other device to produce a computer implementedprocess such that the instructions which execute on the computer, otherprogrammable data processing apparatus, or other device provideprocesses for implementing the functions/acts specified in the block(s)of the flowchart illustrations and/or block diagrams.

The flowchart illustrations and block diagrams in the Figures illustratethe architecture, functionality, and operation of possibleimplementations of systems, methods, and computer program productsaccording to various embodiments. In this regard, each block in theflowchart illustrations or block diagrams may represent a module,segment, or portion of code, which comprises one or more executableinstructions for implementing the specified logical function(s). Itshould also be noted that, in some alternative implementations, thefunctions noted in the block may occur out of the order noted in theFigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. It will also be noted that each block of the block diagramsand/or flowchart illustrations, and combinations of blocks in the blockdiagrams and/or flowchart illustrations, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts, or combinations of special purpose hardware and computerinstructions.

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

We claim:
 1. An optical module comprising: an optical source arranged toproduce an optical signal; a first polarization splitter-rotatorarranged to generate a first source optical signal based at least inpart on the optical signal; a second polarization splitter-rotatorarranged to generate a second source optical signal based at least inpart on the optical signal; a first port arranged to transmit, to afirst device, the first source optical signal and to receive, from thefirst device, a first modulated optical signal, wherein the firstmodulated optical signal has a polarization that is orthogonal to apolarization of the first source optical signal, wherein the firstpolarization splitter-rotator produces a second modulated optical signalbased at least in part on the first modulated optical signal; a secondport arranged to transmit, to a second device, the second source opticalsignal and to receive, from the second device, a third modulated opticalsignal, wherein the third modulated optical signal has a polarizationthat is orthogonal to a polarization of the second source opticalsignal, wherein the second polarization splitter-rotator produces afourth modulated optical signal based at least in part on the thirdmodulated optical signal; a third port arranged to transmit the secondmodulated optical signal to the second device; and a fourth portarranged to transmit the fourth modulated optical signal to the firstdevice.
 2. The optical module of claim 1, further comprising a mirrorarranged to reflect the second modulated optical signal from the firstpolarization splitter-rotator towards the third port.
 3. The opticalmodule of claim 1, further comprising an optical isolator or a Faradayrotator arranged to direct the optical signal from the optical source tothe first polarization splitter-rotator.
 4. The optical module of claim1, wherein a single mode fiber is connected to the first port, whereinthe first source optical signal is transmitted over the single modefiber, and wherein the first modulated optical signal is received overthe single mode fiber.
 5. The optical module of claim 1, wherein theoptical source is a laser diode.
 6. The optical module of claim 1,further comprising a lens that directs the second modulated opticalsignal to the third port.
 7. The optical module of claim 1, wherein theoptical module is a pluggable device that attaches to the second device.8. A method comprising: producing, by an optical source, an opticalsignal; generating, by a first polarization splitter-rotator, a firstsource optical signal based at least in part on the optical signal;generating, by a second polarization splitter-rotator, a second sourceoptical signal based at least in part on the optical signal;transmitting, by a first port and to a first device, the first sourceoptical signal; receiving, by the first port and from the first device,a first modulated optical signal, wherein the first modulated opticalsignal has a polarization that is orthogonal to a polarization of thefirst source optical signal; producing, by the first polarizationsplitter-rotator, a second modulated optical signal based at least inpart on the first modulated optical signal; transmitting, by a secondport and to a second device, the second source optical signal;receiving, by the second port and from the second device, a thirdmodulated optical signal having a polarization that is orthogonal to apolarization of the second source optical signal; producing, by thesecond polarization splitter-rotator, a fourth modulated optical signalbased at least in part on the third modulated optical signal;transmitting, by a third port, the second modulated optical signal tothe second device; and transmitting, by a fourth port, the fourthmodulated optical signal to the first device.
 9. The method of claim 8,further comprising reflecting, by a mirror, the second modulated opticalsignal from the first polarization splitter-rotator towards the thirdport.
 10. The method of claim 8, further comprising directing, by anoptical isolator or a Faraday rotator, the optical signal from theoptical source to the first polarization splitter-rotator.
 11. Themethod of claim 8, wherein a single mode fiber is connected to the firstport, wherein the first source optical signal is transmitted over thesingle mode fiber, and wherein the first modulated optical signal isreceived over the single mode fiber.
 12. The method of claim 8, whereinthe optical source is a laser diode.
 13. The method of claim 8, furthercomprising directing, by a lens, the second modulated optical signal tothe third port.
 14. The method of claim 8, wherein the method isperformed by a pluggable device that attaches to the second device. 15.A system comprising: a source device; a receiver device; and a pluggabledevice attached to the source device, wherein the pluggable devicecomprises: an optical source arranged to produce an optical signal; afirst polarization splitter-rotator arranged to generate a first sourceoptical signal based at least in part on the optical signal; a secondpolarization splitter-rotator arranged to generate a second sourceoptical signal based at least in part on the optical signal; a firstport arranged to transmit, to the receiver device, the first sourceoptical signal and to receive, from the receiver device, a firstmodulated optical signal, wherein the first modulated optical signal hasa polarization that is orthogonal to a polarization of the first sourceoptical signal, wherein the first polarization splitter-rotator producesa second modulated optical signal based at least in part on the firstmodulated optical signal; a second port arranged to transmit, to thesource device, the second source optical signal and to receive, from thesource device, a third modulated optical signal, wherein the thirdmodulated optical signal has a polarization that is orthogonal to apolarization of the second source optical signal, wherein the secondpolarization splitter-rotator produces a fourth modulated optical signalbased at least in part on the third modulated optical signal; a thirdport arranged to transmit the second modulated optical signal to thesource device; and a fourth port arranged to transmit the fourthmodulated optical signal to the receiver device.
 16. The system of claim15, wherein the pluggable device further comprises a mirror arranged toreflect the second modulated optical signal from the first polarizationsplitter-rotator towards the third port.
 17. The system of claim 15,wherein the pluggable device further comprises an optical isolator or aFaraday rotator arranged to direct the optical signal from the opticalsource to the first polarization splitter-rotator.
 18. The system ofclaim 15, wherein a single mode fiber is connected to the first port,wherein the first source optical signal is transmitted over the singlemode fiber, and wherein the first modulated optical signal is receivedover the single mode fiber.
 19. The system of claim 15, wherein theoptical source is a laser diode.
 20. The system of claim 15, wherein thepluggable device further comprises a lens that directs the secondmodulated optical signal to the third port.